Current methods of communication (voice or digital) typically rely upon either installed cables which may be either insulated electric cables of fiber optic cables, or the transmission of energy through the air (e.g. radio frequency, infrared). Installed cables and wires are expensive to install and maintain and are not considered dependable under fire or battle damage conditions. In addition, in such installed cable systems, the number and location of outlets are usually fixed and may not be located at a point where an emergency communication terminal is required on a ship or in a building. Communication via airwaves eliminates the need for installed cables, wires or fiber optic devices; however, such systems have their own set of problems. RF transmissions have difficulty penetrating steel bulkheads in the interior spaces of a ship or building. Also, the possibility of interference with other installed electronic equipment is high and RF transmissions may not be acceptable under certain emission control conditions. U.S. Pat. No. 2,172,066 to L. B. Logsdon - issued Sep. 5, 1939 and U.S. Pat. No. 4,213,199 to Kenneth B. Labaw - issued Jul. 15, 1980, both describe systems for providing an acoustic communications data link by transmitting acoustic energy through the metal framework of a ship of a building structure. Other communication systems employing acoustic energy have been proposed for transmitting the acoustic energy through the rails of a rail system or pipes of a network of piping used for water supply or other plumbing needs.
The above-noted prior art patents and prior acoustic energy signal transmission systems all acknowledge the fact that acoustic energy can be successfully transmitted through structural members. However, these prior art patents and systems do not address a most fundamental requirement of such systems, namely the specific design of the transducer which either puts acoustic energy into a metal structure or receives acoustic energy from the metal structure and converts it to an intelligible electrical signal. In the Labaw U.S. Pat. No. 4,213,199, it is simply stated that "a transducer which in turn is clamped or cemented to the metal frame" is employed to supply the acoustic energy to the metal framework of a ship or other structure which is being used to transmit the acoustic energy as intelligible signals. Thus, in these prior art disclosures, the specific design of a suitable acoustic transducer is not addressed. The development of a rapid and efficient portable means for coupling an acoustic transducer to the metal framework structure of a ship or building has been the major problem associated with the implementation of reliable acoustic information transmission system such as described in the Labaw U.S. Pat. No. 4,213,199 and Logsdon U.S. Pat. No. 2,172,066.
A typical structural member to which an acoustic transducer can be attached for shipboard applications is coated with several layers of paint and perhaps insulation. Previous acoustic transducer designs built and tested by the U.S. Navy required that the insulation be removed, the paint scraped off and the attachment surface sanded and polished to achieve satisfactory coupling of acoustic energy from the transducer to the structural member at a point desired. This "surface preparation" is a time consuming task, requires many tools and the quality of the coupling is highly dependent upon the skill of the operator/technician installing the system. In the case of fire or battle damage conditions, where the establishment of instant communication at a particular location within a ship or a building may be critical, such time consuming approach to the coupling problem is simply impractical.
A coupling of the acoustic transducer must not only be readily and rapidly accomplished, it also must be highly effective and efficient in operation. For fire fighting or shipboard damage control, the entire acoustic signal transducing device must be portable and lightweight such that an individual fire fighter, damage control man, rescue worker, etc., can easily carry the device to the scene of an accident where communications are to be established, without becoming unduly encumbered. Previous acoustic transducers used for communicating through steel structures such as the framework of ships, rails, piping systems, etc., were grossly ineffective and inefficient due to the combination of poor design and poor coupling. Many of the known prior art devices required the use of a relatively large battery pack as a source of electric power which alone weighed approximately one hundred pounds.